1. Field of the Invention
The present invention relates to a method for driving plasma display panels.
2. Description of the Related Art
In a surface discharge AC type panel that typifies plasma display panels (hereinafter abbreviated as “panel”), a number of discharge cells are formed between an oppositely disposed front panel and a rear panel. On the front panel, two or more pairs of display electrodes comprising a scan electrode and a sustain electrode are formed in parallel on a front glass substrate. Further, on the front panel, a dielectric layer and a protective layer are formed in a manner covering the display electrodes. On the rear panel, two or more parallel data electrodes are formed on a rear glass substrate and a dielectric layer is formed covering the data electrodes. In addition, two or more barrier ribs are formed on top of the dielectric layer in parallel to the data electrodes. In addition, a phosphor layer is formed on the surface of the dielectric layer and the sides of the barrier ribs.
The front panel and the rear panel are oppositely disposed and sealed in a manner such that the display electrodes and the data electrodes make a two-level crossing, and a discharge gas is filled in the inner discharge space. Discharge cells are formed on the sections where the display electrodes and the date electrodes face each other in this way. In a panel having such a structure, ultraviolet ray is generated by gas discharge in each of the discharge cells. Color display is enabled by excitation emission of each of Red (R), Green (G) and Blue (B) phosphors with the ultraviolet ray.
As a method for driving a panel, the sub-field method is generally employed. In this method, the period of one field is divided into plural sub-fields and half-tone expression is performed by the combination of the sub-fields to be fired. Among sub-field methods, a drive method in which contrast ratio is improved by reducing the emission of light which is not related to half tone expression is reduced as much as possible is disclosed in Japanese Patent Unexamined Publication No. 2002-351396.
A brief description of the sub-field method is given below. Each of the sub-fields has an initialization period, a writing period and a sustain period. First, in the initialization period, initialization discharge simultaneously takes place in all discharge cells and erases hysteresis of earlier wall charges existing in the individual discharge cells, and wall charges necessary for subsequent writing action are formed. In addition, a priming (a detonator for discharge or an excitation particle) for decreasing a delay in discharge and stably generating writing discharge is generated.
During the subsequent writing period, scanning pulses are sequentially applied to the scan electrodes while applying to the data electrodes writing pulses corresponding to the image signal to be displayed. Selective writing discharge is thus generated between the scan electrodes and data electrodes thereby selectively forming wall charges. During the sustain period, a predetermined number of sustain pulses corresponding to brightness weight are alternately applied to the scan electrodes and sustain electrodes to selectively discharge the discharge cells in which wall charges have been formed by writing discharge thus causing light emission.
In such a panel of conventional method, dispersion of discharge timing occurs from discharge cell to discharge cell depending on the status of display. As a result, the emission intensity may vary from discharge cell to discharge cell and a screen having a region of brightness non-uniformity may be produced.